<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>这是标签选择器</title>
    <style>
        p{font-weight: bold;
            text-align: center;
            color: red;}
    </style>
</head>
<body>
<p id='test' class='title'>Hello world!</p>
</body>
</html>